The “WP-20 Mini-Synth Sound Effects Synthesizer” is probably the best project out there for getting started in Synth-DIY proper. It packs all the basic elements of modular synth design including a control voltage input into a relatively compact circuit. Released back in 1980 by Waveform Processing, the project has no formal technical support but remains well documented. From the original manual -
The WP-20 Sound Effects Synthesizer does just what it’s name implies. It creates sounds synthetically by means of electronics. It comes very close to imitating many real sounds and can
also create sounds that do not occur in real life. It performs this magic through the use of an oscillator, bandpass filter, envelope generator, low frequency oscillator, amplifier and a white noise source.
The versatility of the WP-20 comes from the fact that several of it’s circuits are ‘Voltage Controlled’. The frequency of the oscillator, for example, may be varied manually by turning one of the oscillator control knobs on the front panel. Turning the knob varies a voltage in the oscillator circuit, thereby changing it’s frequency.
Instructions including links to circuit baord image and examples – WP-20 manual on MusicfromOuterSpace.com
If you do choose to build one, you can find more helpful info on the Electro-Music forums which are frequented by many wise and friendly synth makers.
The WP was one of my first projects, and I still love using it –
In the Maker Shed:
Arduino Pocket Piano Synth Kit